Surgical needles and attached sutures are well known in the art. Surgical needles typically have a distal pointed end and a proximal suture mounting end. The suture mounting end can have several structural configurations for receiving a suture tip, including channels and blind holes. The distal end of a suture is typically mounted to the proximal end of a surgical needle in several ways. For example the distal end or tip of the suture may be inserted into a channel, and the channel is then mechanically swaged to lock the suture in the channel. Or, the distal end or tip of a suture may be mounted into a bore hole drilled into the proximal end of a needle. The proximal end of the needle is then mechanically swaged such that the suture end is mechanically locked into the bore hole. Alternatively, sutures may be mounted to surgical needles using adhesives, epoxies, shrink tubing and other known mounting techniques.
The use of blind bore holes to mount sutures to surgical needles has become the mounting method of choice for many types of surgical needles. The needles having suture mounted in this manner may have less resistance to penetration when moved through tissue. Blind bore holes are typically drilled into the proximal ends of needles using one of two conventional methods. One method of drilling surgical needles is to use mechanical drills. The other method of drilling blind bore holes is to use lasers. Mechanical drilling is known to have several disadvantages including mechanical alignment, tool wear, constant adjustments, the inability to drill small diameter holes, and relative slowness of the mechanical drilling process. The use of laser drilling overcomes many of these problems. The laser uses a beam of light energy to form the blind bore hole by liquefying the metal and causing it to be expelled from the proximal end of the needle. Accordingly, in laser drilling there is no mechanical contact with needle by the drilling apparatus, tool wear is not a problem, alignment problems and adjustments are minimized, and drilling is considerably more time effective, allowing for high production throughput.
Although the use of conventional laser systems to drill surgical needles has many advantages, there are also some problems which are attendant with their use. Laser drilling equipment is typically more sophisticated and complex than mechanical drilling equipment and requires highly skilled operators. In addition, the laser drilling may produce a bore hole which does not have an entirely smooth interior surface because of residual slag resulting from the expulsion of the molten metal. The slag may interfere with the insertion of a suture into a bore hole.
It is known that to produce a smooth bore hole it is desirable to remove metal from a bore hole through evaporation and plasma formation rather than a melting process. This can be done by using pulsed Nd-YAG lasers. Such lasers produce a train of short pulses having sufficient energy to remove small amounts of material with each pulse, thereby producing a high quality bore hole. The duration of the pulses is typically in the 10 microseconds to 100 micro seconds range.
Presently, short pulses for drilling surgical needles are produced using a conventional flash lamp pumped Nd-YAG laser as an oscillator to produce an optical pulse range from 200 microseconds to 600 microseconds duration. This optical pulse is then intensity modulated by an electro-optical modulator or similar device into a plurality of short pulses (i.e., a pulse train). The duration of these short pulses and their frequencies are controlled by the modulator parameters. The pulse train then enters a conventional flash lamp pumped Nd-YAG amplifier and is amplified to produce a high power intensity beam. The high power intensity beam is then focused on the rear or proximal end face of a surgical needle to drill a blind hole into the proximal end of the needle.
Because of the inherent limitations of flash lamp pulsing, the production of short pulses requires modulation of the main pulse by means of an electro-optical modulator, which in turn requires an optical polarizer and analyzer. The addition of these optical devices along the path of the laser beam causes the loss of some optical energy, and is associated with some difficulty in keeping the optical devices optically aligned in the manufacturing environment. The electro-optical modulator (Pockles Cell) requires the use of high voltage electronics which in turn require high maintenance and extensive safety precautions. The flash lamp pumped laser oscillator and amplifier use both high voltage power supplies and capacitor banks to store energy for discharging into the flash lamp. The flash lamp is believed to be an inefficient way of pumping a laser rod, since most of the energy is dissipated in the form of heat which must be removed by a cooling system. The power supply, capacitor banks, and cooling system require significant amounts of space, maintenance and troubleshooting. The heat dissipated in the laser rod from flash lamp operation also causes thermal lensing of the rod, which deteriorates the quality of the laser beam. Another problem observed with the existing flash lamp pumped method is usable flash lamp life. The average flash lamp may have a life of about 500 to 600 hours. This requires shutting down the laser drilling system every 600 or so hours to replace the flash lamp thereby interrupting production, and necessitating maintenance and repair.
Accordingly, there is a need in this art for improved pulsed laser systems which overcome the disadvantages of a flash lamp pulsing system.